With the development of high resolution display technologies, sizes of the pixels are gradually decreased. To maintain the aperture ratio, metal electrodes of the pixels and line width of the color filter black matrix (BM) have to be narrower as well. However, it is difficult to realize narrower line width in known photolithography processes due to the diffraction effect of light.
Currently, to overcome the influence of the diffraction effect, a method realizes narrower line width by way of a sawtooth-shaped slit as illustrated in FIG. 1. The line width is adjusted by adjusting a width a, a gap b and an angle θ. The advantage of the method lies in that the narrower line width effect can be realized by simply changing the layout design of the mask slits. However, it has the disadvantage of having too many burrs, not smooth and lacking corner design. In fact, a straight line design is normally combined with the sawtooth design. That is, the straight line design is used in a direction not requiring narrower line width while the sawtooth design is inserted in the straight line design for a direction requiring narrower line width as illustrated in FIG. 2. The joining part between the two designs lacks smooth connection design, making the line width at the corner too narrow as to being etched and causing broken-line defect. Furthermore, when both directions require the narrower line width design, the design as FIG. 2 cannot meet the requirement of having narrower line width design in both directions.